An example of a machine with multiple electrical conductors that may need to be tested for electrical faults such as unacceptable current leakage is a paving machine. Typical paving machines include a tractor for providing mobility and power, a hopper containing a supply of a bituminous aggregated mixture or asphalt, and a screed which lays the asphalt paving material onto an area to be paved in a strip of uniform thickness. The tractor typically includes a combustion engine configured to power operations of the paving machine, and the engine may be any of a variety of known power plants that may include gas turbine engines, natural gas powered engines, diesel engines, and gasoline engines. The asphalt paving material is heated and is applied when it has a plastic consistency so that it may be easily applied in a layer of uniform thickness. In a repaving operation, the new asphalt material may be laid upon the old surface of the roadway. It has been found that the new asphalt material adheres to the old road surface much better when the old road surface is warm. Poor results are obtained when the new asphalt material is applied upon a cold roadway. For this reason, specific temperature conditions exist under which paving must occur to ensure pavement quality. This limits the length of the paving season and the productivity on days when paving crews must wait for the temperature to rise.
A screed assembly typically includes a base portion and may include one or more extension portions, each of these portions having steel screed plates mounted to the screed portions in such a manner that the plates both smooth and compress the deposited paving material, leaving behind a mat of the desired thickness. The screed plates are typically heated to prevent the asphalt material from clinging to the steel plates. In modern screed assemblies, the screed plate heaters are commonly implemented in the form of resistive electrical heaters that can be optimally positioned on or near the screed plates. Screed plates may also be heated by gas or other combustible fuel heaters. It is important to maintain a proper screed plate temperature. If the screed plates are either too hot or too cold, a poor finish will be obtained in the resulting pavement mat. In a simple screed having only base screed portions, each of the base screed portions typically includes both a heater and a temperature sensor. In such a system, each of the base screed plates may be individually temperature controlled according to feedback received from the associated temperature sensor. A wider screed requires more heaters, and the heaters are generally arranged into independent heating zones. Electric power to the heaters is controlled by a screed power module (SPM). During the paving process it is important to identify the location of any faulty heating elements as quickly as possible to avoid wasting asphalt material. If particular heating elements fail, asphalt may stick to the screed in the area that is allowed to cool, wasting material and resulting in a mat of asphalt that is not of the desired quality and uniformity.
During operation of a paving screed, an undesirable situation arises when the insulation or other portion of an energized heating element fails and the electrical source is shorted or leaks current to the housing of the chassis of the paving machine. In addition to potentially causing the failure of a heating element and the resulting waste of asphalt material described above, damage to the paving machine or systems or other potentially hazardous situations may result. As a result, there is a need to identify the location of a faulty heating element amongst the many heating elements present, and perform the necessary repairs in response thereto. A wider screed may exacerbate this problem as a result of the additional zones and heaters needed to heat the additional area of base screed plates.
One method of detecting faults in an electrical circuit is described in U.S. Pat. No. 5,574,346 issued to Chavan et al. on Nov. 12, 1996 (the '346 patent). A winding fault detection circuit monitors voltage drops in the phase windings of a motor and compares the voltage drops with reference voltages to determine if the motor is out of normal operating range parameters and if a valid fault exists. If a valid fault exists, a circuit driving the motor is interrupted.
Although the fault detection circuit of the '346 patent may interrupt operation when a winding fault is detected, it may be overly complex, costly, and difficult to implement. For example, the fault detection circuit requires comparator logic to monitor the windings of each phase of the motor and to compare the voltage drops across each winding to a high reference voltage and a low reference voltage. In addition, the outputs of the comparator logic must be sequentially selected and provided to fault logic in accordance with the excitation of respective phase windings and the angular position of the motor. Only at this point may analysis be made as to whether a winding fault is present.
The present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems with existing technology.